The invention relates to an illuminator for an image acquisition system, in particular for acquiring images comprising optical information.
Image acquisition systems are known comprising “an optical apparatus for acquiring images” and an “illuminator”, associated with this optical apparatus, for acquiring images of an object arranged on a supporting surface and processing these images to extract “optical information” from these images.
In particular, for acquisition systems of fixed type, the optical apparatus and the illuminator are connected to a supporting base, the position of which does not vary during operation of the optical apparatus.
Acquisition systems of this type are made for use without human action (“unattended systems”), to acquire images of objects that can be in transit on a conveyor belt (or other movement means) in certain production plants or package sorting centres, or can be arranged manually by an operator in a preset workstation dedicated to acquisition, in other productive, or conveying and logistic applications.
Such acquisition systems are usually located from 0.3 to 3 meters from the plane of the image to be acquired and can be positioned with the optical apparatus facing downwards to acquire images from above or horizontally to acquire images frontally and are used advantageously, for example, in production plants for automatic identification for the purposes of tracing and sorting products (for example tyres) during the various processing steps, for measuring without contact, selecting and orienting industrial items, inspecting materials for the purpose of identifying defects or for dimensional checks, monitoring, biometric recognition and checking accesses. If the apparatus faces downwards, for acquisitions from above, the optical apparatus is often much higher then an operator.
The expression “optical apparatus for acquiring images” refers to an optoelectronic apparatus for acquiring images that is able to acquire images of an object, and in particular to process these images in such a manner as to extract from them the geometrical and/or shape features of the object (for example distance, volume, overall dimensions of the object), or comprising optical information, associated with this object. The expression “optical information” means any graphic representation that constitutes information, whether coded or uncoded.
One example of coded information is an optical, linear or two-dimensional code, in which the data are coded identifying the object with which the optical code is associated. The information is coded by suitable combinations of elements of a preset shape, for example squares, rectangles or hexagons, of a dark colour (normally black) separated by light elements (spaces that are normally white), and barcodes, stacked codes and two-dimensional codes in general, colour codes, etc, are known.
The term “optical information” further comprises, more in general, also other graphic shapes, which included printed or handwritten characters (letters, numbers, etc) and particular shapes (so-called “patterns”), such as, for example, stamps, logos, signatures, finger prints, etc and any graphic representation that is detectable not only in the field of visible light but also along the entire wavelength comprised between infrared and ultraviolet.
The optical apparatus comprises a body on which an electronic sensor is arranged, for example an array of photosensitive elements of linear or matrix type for example of the CCD or CMOS type, and suitable optical receiving means fixed removably to the body, for example with a “C-Mount” consisting of one or more lenses, by means of which the sensor is suitable for receiving the diffused light from the object to be acquired.
The optical apparatus further comprises a control device, for commanding the acquisition of the image and switching on of the illuminator, as will be illustrated better below, and for processing the acquired image in order to extract the feature of interest from the image and/or decode a piece of acquired coded information. Optical apparatuses of this type are known as linear or matrix cameras, and in the case of acquiring images comprising optical information, these optical apparatuses are also known as “imagers” or “smart cameras”.
“Field of view” is to be understood as an acquisition field of the optical apparatus, i.e. a preset area inside which the images of the object can be acquired, which is located within a focusing range and for which, along the optical axis of the optical means, it is possible to define a depth of field. It is observed that for acquisition systems of fixed type the optical apparatus usually comprises manually adjusted and fixed-focus optical means, in the sense that focusing and adjusting the aperture of the diaphragm can be achieved by operator only by means of adjusting ring nuts with which the optical means is provided. The illuminator comprises illuminating means comprising a plurality of single electronically controllable light emitters, and i.e. a plurality of LEDs (light emitting diodes), which are typically arranged around the optical means of the optical apparatus, to illuminate appropriately the object the image of which is to be acquired.
In particular, the illuminator has to illuminate the entire acquisition field of view of the optical apparatus with which it is associated, in all the corresponding depth of field.
The illuminator is typically activated by the control device of the optical apparatus with which it is associated and with which it is electrically connected. For example, a digital signal can be provided of a dedicated contact of the connector means interface arranged between the illuminator and the optical apparatus which, normally at a low logic value, can switch to a high logic value when the control device of the optical apparatus intends to switch on the illuminator.
The illuminator and the optical acquisition apparatus can in this manner be activated by the control device at a preset frequency, if the image acquisition method requires images to be acquired continuously, or, alternatively, the illuminator can be activated only when one or more presence sensors detect the presence of the object in the field of view of the optical acquisition apparatus or, in another alternative configuration, when an object is identified in the field of view following the analysis of the contents of a first series of images acquired preliminarily with the illuminator switched off.
Over time, as the production technology of the CCD or CMOS has become increasingly refined and in other words the number of pixels of the image sensors with which it is possible to equip the optical apparatus has increased, the field of view and the depth of field of the optical apparatus have become increasingly extended and it has therefore become necessary to increase the power of the illuminator to prevent the optical apparatus acquiring poorly lighted images from which it is difficult to extract the optical information.
To increase this lighting power, increasing the number of LEDs with which the illuminator is equipped is known. This increase in the number of LEDs nevertheless raises the question of the dissipation of heat produced by the LEDs during operation, the LEDs being at risk of damage from a possible increase in the operating temperature or the working life of the LEDs may be significantly reduced if the operating temperature is high.
An increasingly appreciated and therefore even more important requirement for an image acquisition system for industrial applications is that it has minimal overall dimensions when the optical apparatus and the illuminator are associated. A configuration with minimal overall dimensions is a configuration in which in the direction parallel to the optical axis the dimension of the acquisition system is about equal to that of the optical apparatus and in which on the plane perpendicular to the optical axis the overall dimensions are near those of the area occupied by the optical means and by the illuminating means. In other words, the acquisition system has to be as compact as possible and of small overall dimensions.
Thus, in order to maintain compact overall dimensions of the image acquisition system, whilst at the same time ensuring suitable dissipation of the heat produced by the LEDs of the illuminator, image acquisition systems are known comprising a single integrated housing containing both the optical apparatus and the illuminator, having a frontal face provided with lighting LEDs. These LEDs can be arranged in a ring around an opening of a front wall of the frontal face of the illuminator, inside which the optical means is received, or they can be arranged symmetrically on a side opposite this opening, if the housing of the acquisition system is shaped and has a frontal face of rectangular shape. In order to ensure that the image acquisition system is compact, the end of the optical means is substantially coplanar with the frontal wall on which the illuminating LEDs are arranged.
Further, ring illuminators are known that have a separate housing from the housing of the optical apparatus and can be adapted to optical apparatuses of different type. Such illuminators comprise a housing with external and internal tubular coaxial elements and the internal tubular element is typically suitable for receiving internally, when the illuminator is associated with the optical apparatus, the optical means of the apparatus. The housing of the illuminator is so shaped as to receive the optical means of the optical apparatus, in such a manner as to surround the housing of the apparatus without constituting a further overall dimension. The frontal face of the illuminator is shaped as a circular crown delimited respectively by the external and internal tubular element, substantially coplanar with the end of the optical means.
One drawback of the known illuminators disclosed above is that they do not permit rapid access to the optical means, when they are associated with the optical apparatus in the minimal overall dimensions configuration, inasmuch as the illuminators surround the optical apparatus completely.
If an operator has to replace the optical means installed in an acquisition system located in the definitive work position with others of another type, or has to adjust focussing or the diaphragm for the depth of field of such optical means, it is necessary to dismantle the illuminator from the optical apparatus. If the optical apparatus and the illuminator have different housings, it is sufficient for only the illuminator to be dismantled from the apparatus. On the other hand, it there is a single integrated housing both for the optical apparatus and for the illuminator, the entire acquisition system has to be dismantled. Nevertheless, in both cases, this dismantling is long and adjustment is difficult, so preferably this adjusting is executed on a specific test bench, if possibly a laboratory and specialised technicians are available. The acquisition system is again located in its acquisition position only at the end of adjusting and only when perfectly functioning, for example at the new focusing distance.
Another drawback of the acquisition systems illustrated so far is that adjusting the optical apparatus requires the present of a dedicated screen at the disposal of the operator.
In fact, in addition to the difficulty of access to the optical means due to the presence of the housing of the illuminator and/or of the optical apparatus, adjusting focusing and the conditions for correct acquisition of images cannot be performed with the necessary precision without the help of a dedicated consultation screen for the operator (for example a screen of a user interface device). In fact, sample images have to be acquired by the optical apparatus, the images have to be displayed on the consultation screen and the images have to be controlled by the operator, who has to decide when to terminate the focusing adjustment because the acquired sample image is clear.
In other known solutions, in order to guide the actions of the operator, on the consultation screen, together with the acquired images, or alternatively to them, some indexes are shown that measure focusing quality. These indexes are calculated by the image acquisition and processing apparatus.
The presence of the consultation screen, which shows the operator the acquired images and/or the focusing quality indexes it is therefore necessary to adjust the focus of the optical means of the apparatus.
In addition, after adjusting focusing, the operator must be able to check also other acquisition conditions, i.e. the operator has to be able to check that the coded information in the acquired image is correctly decodeable by the optical apparatus in such a manner as to otherwise vary other parameters of the optical apparatus and/or of the illuminator.
In some already known image acquisition systems, it is observed that the optical apparatus comprises visual status indicating means in the form of status LEDs arranged in the body of the optical apparatus and one or more pushbuttons associated therewith. By means of the pushbutton/pushbuttons and by checking the visual status indicating means, the optical apparatus is configurable in an initial step of setting the operating parameters of the apparatus, also without the help of an additional consulting screen. Nevertheless, if the optical apparatus is associated with an illuminator with a very bulky frontal face these status LEDs, which are used as visual status indicating means and/or as reading outcome indicating means during adjustment of focusing and in a work step of the optical apparatus, are nevertheless difficult for an operator to see. If the acquisition system is located in its acquisition position high up, at about 0.5-2 meters from the operator, the status LEDs of the optical apparatus are not visible because they are obscured by the presence of the lighting system.
The compactness constraint of the acquisition system would also make unusable, if applicable, visual indicating means of reading outcome that is typical of portable coded information devices if they were integrated into the optical apparatus of the image acquisition system. Such indicating devices, in fact, which are displayable as for example a green or red light beam projected to the acquisition plane, should be located on the sides of the optical means and would thus impose wide opening in the front wall of the body of the illuminator, of a dimension certainly greater than the minimum necessary for receiving the optical means. This would increase the overall dimensions of the illuminator and thus of the image acquisition system.
The distance at which the acquisition system is installed also raises a further problem in addition to those listed so far inasmuch as the acquisition area of the optical apparatus and thus the field of view can be difficult for an operator to delimit. This entails consequent lengthening of the time required to successfully process each single image as the acquired image can also comprise only part of the coded information unless it is correctly framed. The acquisition of the image would thus have to be repeated. This results in further extension of total adjusting time and configuration time of the acquisition system and becomes a critical element for image acquisition systems in which an object is arranged manually by an operator in a preset position dedicated to acquisition. Although this workstation is marked for the operator the absence of indications coming from the acquisition system on the position of the field of view can require a very long time for obtaining a successfully processed image.
One object of the invention is to overcome the drawbacks of known illuminators for image acquisition systems.
A further object is to provide an illuminator that, when it is associated with the optical apparatus, permits easy access to adjust the optical means of the optical apparatus, in particular easy access to the focusing ring nut and to the ring nut for adjusting the diaphragm aperture.
Another object is to provide a different type of illuminator that improves the installation, use and maintenance of an acquisition system, avoiding involving the operator in lengthy acquisition system configuration and adjusting, if the optical means of the optical apparatus have to be replaced and/or adjusted after the optical apparatus has already been associated with the illuminator.
Still another object is to provide a different type of illuminator that improves the indications to an operator in the case of acquisition systems with a fixed workstation and operator, who conveys to this workstation the object the image of which has to be acquired.
These objects and still others are all achieved by an illuminator for an image acquisition system as defined according to one or more of the claims set out below.